[Enhancement]: Allow Drag&Drop of files/folders into another folder

[pkerschbaum]

Motivation

As other file explorers can do, it should be able to select multiple files/folders and move them into another folder via Drag&Drop.
It would be even better if this file explorer could "react" to files/folders dropped into it from the outside, e.g. from the MacOS Finder or Windows File Explorer.

See this screenshot for illustration purposes:

Implementation Notes

There is already a onDragStart handler on resource rows / resource tiles which allows to drag the selected resource outside of the file explorer into other applications. E.g. if a .pdf file is dragged from the file explorer to a web browser, the browser opens the PDF file.
See these lines of code:

file-explorer/src/ui/resources-table/ResourcesTable.tsx

Lines 387 to 390 in 3495976

	onDragStart: (e: React.DragEvent<HTMLTableRowElement>) => {
	e.preventDefault();
	startNativeDnDForSelectedResources();
	},

The implementation of startNativeFileDnD is based on the Electron native file drag & drop API (https://www.electronjs.org/docs/latest/tutorial/native-file-drag-drop). It runs in the main process here:

file-explorer/src/platform/electron/ipc/electron-main/file-drag-start.ts

Lines 1 to 25 in 3495976

	import { ipcMain, IpcMainEvent, Item } from 'electron';
	import invariant from 'tiny-invariant';
	import {
	IpcFileDragStart,
	FILEDRAGSTART_CHANNEL,
	} from '@app/platform/electron/ipc/common/file-drag-start';
	import { OUTLINE_INSERT_DRIVE_FILE_ICON_PATH } from '@app/static-resources-main';
	export function registerListeners(): void {
	ipcMain.on(FILEDRAGSTART_CHANNEL, fileDragStartHandler);
	}
	function fileDragStartHandler(
	e: IpcMainEvent,
	{ fsPaths }: IpcFileDragStart.Args,
	): IpcFileDragStart.ReturnValue {
	invariant(fsPaths.length > 0);
	const startDragArg: Omit<Item, 'file'> = {
	files: fsPaths,
	icon: OUTLINE_INSERT_DRIVE_FILE_ICON_PATH,
	};
	// @ts-expect-error -- electron typings have the property "file" defined as required, although that is actually not necessary (https://www.electronjs.org/docs/latest/api/web-contents#contentsstartdragitem)
	e.sender.startDrag(startDragArg);
	}